Plasma Physics
New submissions
[ showing up to 2000 entries per page: fewer | more ]
New submissions for Fri, 17 May 24
- [1] arXiv:2405.09587 [pdf, other]
-
Title: BxC Toolkit: Generating Tailored Turbulent 3D Magnetic FieldsSubjects: Plasma Physics (physics.plasm-ph); High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR); Space Physics (physics.space-ph)
Turbulent states are ubiquitous in plasmas and the understanding of turbulence is fundamental in modern astrophysics. Numerical simulations, which are the state-of-the-art approach to the study of turbulence, require substantial computing resources. Recently, attention shifted to methods for generating synthetic turbulent magnetic fields, affordably creating fields with parameter-controlled characteristic features of turbulence. In this context, the BxC toolkit was developed and validated against direct numerical simulations (DNS) of isotropic turbulent magnetic fields. Here, we demonstrate novel extensions of BxC to generate realistic turbulent magnetic fields in a fast, controlled, geometric approach. First, we perform a parameter study to determine quantitative relations between the BxC input parameters and desired characteristic features of the turbulent power spectrum, such as the extent of the inertial range, its spectral slope, and the injection and dissipation scale. Second, we introduce in the model a set of structured background magnetic fields B0, as a natural and more realistic extension to the purely isotropic turbulent fields. Third, we extend the model to include anisotropic turbulence properties in the generated fields. With all these extensions combined, our tool can quickly generate any desired structured magnetic field with controlled, anisotropic turbulent fluctuations, faster by orders of magnitude with respect to DNSs. These can be used, e.g., to provide initial conditions for DNS simulations or easily generate synthetic data for many astrophysical settings, all at otherwise unaffordable resolutions.
- [2] arXiv:2405.09705 [pdf, other]
-
Title: The Realization of a Gas Puff Imaging System on the Wendelstein 7-X StellaratorAuthors: J.L. Terry, A. von Stechow, S.G. Baek, S.B. Ballinger, O. Grulke, C. von Sehren, R. Laube, C. Killer, F. Scharmer, K.J. Brunner, J. Knauer, S. Bois, the W7-X TeamComments: 30 pages, 23 figures, submitted to Review of Scientific InstrumentsSubjects: Plasma Physics (physics.plasm-ph)
A system for studying the spatio-temporal dynamics of fluctuations in the boundary of the W7-X plasma using the Gas-Puff Imaging (GPI) technique has been designed, constructed, installed, and operated. This GPI system addresses a number of challenges specific to long-pulse superconducting devices like W7-X, including the long distance between the plasma and the vacuum vessel wall, the long distance between the plasma and diagnostic ports, the range of last closed flux surface locations for different magnetic configurations in W7-X, and management of heat loads on the system's plasma-facing components. The system features a pair of "converging-diverging" nozzles for partially collimating the gas puffed locally $\approx$135 mm radially outboard of the plasma boundary, a pop-up turning mirror for viewing the gas puff emission from the side (also acting as a shutter for the re-entrant vacuum window), and a high-throughput optical system that collects visible emission resulting from the interaction between the puffed gas and the plasma and directs it along a water-cooled re-entrant tube directly onto the 8 x 16 pixel detector array of the fast camera. The DEGAS 2 neutrals code was used to simulate the H$_\alpha$ (656 nm) and the HeI (587 nm) line emission expected from well-characterized gas-puffs of H$_2$ and He and excited within typical edge plasma profiles in W7-X, thereby predicting line brightnesses used to reduce the risks associated with system sensitivity and placement of the field of view. Operation of GPI on W7-X shows excellent signal to noise ratios (>100) over the field of view for minimally perturbing gas puffs. The GPI system provides detailed measurements of the 2-dimensional (radial and poloidal) dynamics of plasma fluctuations in the W7-X edge, scrape-off layer, and in and around the magnetic islands that make up the island divertor configuration employed on W7-X.
- [3] arXiv:2405.09773 [pdf, ps, other]
-
Title: Advanced Tokamak: The Strongly Reversed Central Magnetic Shear ProfileAuthors: Keanu NakamuraComments: 27 pages, 13 figures, 58 referencesSubjects: Plasma Physics (physics.plasm-ph)
This review article will offer a qualitative overview of the strongly reversed shear profile for steady-state operation in tokamaks. For a steady-state reactor to be commercially viable, it is necessary to have a large bootstrap fraction. Currently, there appears great potential in an Advanced Tokamak (AT) regime, namely the hollow current profile (strongly reversed shear). This mode is characterized by high poloidal beta, broad current profiles, strong internal and edge pressure gradients, and relatively good magnetohydrodynamic (MHD) stability against Neoclassical Tearing Modes (NTMs) and ballooning modes. The n=1 and n=2 kink modes, resistive wall modes, and double tearing modes are of concern in the reversed shear profile, and avoidance and/or suppression of these modes is necessary. Although there is a relatively low net plasma current in the reversed shear, the regime appears to have excellent energy confinement properties due to the naturally occurring Internal Transport Barriers (ITBs) caused by the substantial bootstrap currents, and Edge Transport Barriers (ETBs), which can form from ELM-free H-Mode (QH-Mode), to form the Quiescent Double Barrier (QDBs). The reversed shear can be generated by freezing the current profile, through MHD effects or substantial heating and/or current drive during the current ramp up phase, and is sustained by off-axis non-inductive current drive sources, such as the Neutral Beam Current Drive (NBCD), Lower Hybrid Current Drive (LHCD), and Helicon Current Drive (HCD). Experimental results by DIII-D, JT-60U, ASDEX Upgrade, JET, PBX-M, COMPASS-D, and K-STAR, simulation models and codes, such as Lower Hybrid Simulation and STELION, and theoretical reactors, such as ARIES-RS, ARIES-AT and SSTR are referenced.
- [4] arXiv:2405.09837 [pdf, other]
-
Title: On the edge turbulence in a DTT-like tokamak plasmaComments: 34 pages, 26 figures and 6 multi-panel figuresSubjects: Plasma Physics (physics.plasm-ph)
Turbulent transport provides the main contribution to particle and energy losses in tokamak plasmas, which control is of paramount importance for forthcoming reactors such as the Divertor-Tokamak-Test (DTT) facility under construction at ENEA Frascati. In this work we investigate the characteristic features of drift turbulence at the plasma edge through 3D electro-static fluid simulations. We outline the crucial role of the diffusion coefficient for the emerging turbulent spectra and for the excitation of vortex structures or zonal flows. Moreover, the impact of adding a poloidal magnetic component is discussed considering also a radial shear, and the emergence of anisotropic spectral features is emphasized. The analysis is extended to the case with Dirichlet boundary conditions along the radial direction, instead of the periodic ones usually employed in such kind of analyses.
- [5] arXiv:2405.09912 [pdf, ps, other]
-
Title: Driver at 10 MJ and 1 shot per 30 minutes for inertial confinement fusion at high gain: efficient, compact, low laser-plasma instabilities, multi-color, low-cost, applicable to multiple fusion schemesSubjects: Plasma Physics (physics.plasm-ph); High Energy Physics - Experiment (hep-ex)
The ignition at the National Ignition Facility (NIF) set off a global wave of research on the inertial fusion energy (IFE). However, IFE requires a necessary target gain G of 30-100, while it is hard to achieve the fusions at such high gain with the energy, configuration, and technical route of the NIF. We will present a conceptual design for the next generation laser driver of 10 MJ, 2~3 PW at the laser wavelength of 0.353 micrometer (or 0.353 micrometer, then the energy and power can be higher), and 1 shot per 30 minutes, which is efficient, compact, low-cost, low laser-plasma instabilities, applicable to multiple laser fusion schemes, and aiming for G > 30.
- [6] arXiv:2405.10227 [pdf, other]
-
Title: Experimental Validation of Collision-Radiation Dataset for Molecular Hydrogen in PlasmasAuthors: Keisuke Fujii, Keiji Sawada, Kuzmin Arseniy, Motoshi Goto, Masahiro Kobayashi, Liam H. Scarlett, Dmitry V. Fursa, Igor Bray, Mark C. Zammit, Theodore M. BiewerSubjects: Plasma Physics (physics.plasm-ph); Chemical Physics (physics.chem-ph)
Quantitative spectroscopy of molecular hydrogen has generated substantial demand, leading to the accumulation of diverse elementary-process data encompassing radiative transitions, electron-impact transitions, predissociations, and quenching. However, their rates currently available are still sparse and there are inconsistencies among those proposed by different authors. In this study, we demonstrate an experimental validation of such molecular dataset by composing a collisional-radiative model (CRM) for molecular hydrogen and comparing experimentally-obtained vibronic populations across multiple levels. From the population kinetics of molecular hydrogen, the importance of each elementary process in various parameter space is studied. In low-density plasmas (electron density $n_\mathrm{e} \lesssim 10^{17}\;\mathrm{m^{-3}}$) the excitation rates from the ground states and radiative decay rates, both of which have been reported previously, determines the excited state population. The inconsistency in the excitation rates affects the population distribution the most significantly in this parameter space. On the other hand, in higher density plasmas ($n_\mathrm{e} \gtrsim 10^{18}\;\mathrm{m^{-3}}$), the excitation rates \textit{from} excited states become important, which have never been reported in the literature, and may need to be approximated in some way. In order to validate these molecular datasets and approximated rates, we carried out experimental observations for two different hydrogen plasmas; a low-density radio-frequency (RF) heated plasma ($n_\mathrm{e}\approx 10^{16}\;\mathrm{m^{-3}}$) and the Large Helical Device (LHD) divertor plasma ($n_\mathrm{e}\gtrsim 10^{18}\;\mathrm{m^{-3}}$)... [continued]
- [7] arXiv:2405.10298 [pdf, other]
-
Title: Heavy-element damage seeding in proteins under X-ray free electron laser illumination conditionsSubjects: Plasma Physics (physics.plasm-ph); Biological Physics (physics.bio-ph); Computational Physics (physics.comp-ph)
The emerging technique of serial femtosecond X-ray crystallography (SFX) can be used to study the structure and dynamics of biological macromolecules to high spatial and temporal resolutions. An ongoing challenge for SFX is the damage caused by the ultrabright X-ray free electron laser pulse. Though it is often assumed that sufficiently femtosecond pulses `outrun' radiation damage, in reality electronic damage processes commence during exposure. We model the electronic damage to protein nanocrystals using a plasma model that tracks the continuous changes to the energy distribution of the unbound electrons. Tracking the continuous energy distribution is of particular importance for distinguishing the influence of differing elements on secondary damage processes. Heavy atoms have a ubiquitous but small presence in protein targets - typically as integral components of the macromolecule and as salts in the solvent. We find that these atoms considerably influence the simulated ionization and scattering behavior of realistic targets due to their rapid seeding of secondary ionization processes. In lysozyme, even the presence of native sulfur atoms significantly contributes to theoretical measures of damage-induced noise for >= 6 keV, 15 fs pulses. Contributing to the effect is that heavy atoms seed `intermediate' energy electron cascades that are particularly effective at ionizing the target on the femtosecond timescale. In addition, the disproportionate effect of heavy atoms means the damage to a protein crystal can be sensitive to their presence in the solvent. Outside of reducing the concentration of heavy atoms in the target, these results suggest the dose limits of SFX targets will be higher where the ionization of deep >~ 6 keV absorption edges is minimized, or, to a lesser extent, when such edges are only ionized with X-rays >> 2 keV above their binding energy.
Cross-lists for Fri, 17 May 24
- [8] arXiv:2405.09618 (cross-list from astro-ph.HE) [pdf, other]
-
Title: Electron heating in high Mach number collisionless shocksAuthors: Arno Vanthieghem, Vasileios Tsiolis, Anatoly Spitkovsky, Yasushi Todo, Kazuhiro Sekiguchi, Frederico FiuzaComments: 10 pages, 6 figures, 1 table; Accepted for publication in Physical Review LettersSubjects: High Energy Astrophysical Phenomena (astro-ph.HE); Plasma Physics (physics.plasm-ph)
The energy partition in high Mach number collisionless shock waves is central to a wide range of high-energy astrophysical environments. We present a new theoretical model for electron heating that accounts for the energy exchange between electrons and ions at the shock. The fundamental mechanism relies on the difference in inertia between electrons and ions, resulting in differential scattering of the particles off a decelerating magnetically-dominated microturbulence across the shock transition. We show that the self-consistent interplay between the resulting ambipolar-type electric field and diffusive transport of electrons leads to efficient heating in the magnetic field produced by the Weibel instability in the high-Mach number regime and is consistent with fully kinetic simulations.
Replacements for Fri, 17 May 24
- [9] arXiv:2402.02180 (replaced) [pdf, other]
-
Title: Phase space eigenfunctions with applications to continuum kinetic simulationsComments: 51 pages, 26 figures, 4 appendicesSubjects: Plasma Physics (physics.plasm-ph)
- [10] arXiv:2403.02776 (replaced) [pdf, other]
-
Title: Ultrahigh Resolution X-ray Thomson Scattering Measurements at the European XFELAuthors: Thomas Gawne, Zhandos A. Moldabekov, Oliver S. Humphries, Karen Appel, Carsten Bähtz, Victorien Bouffetier, Erik Brambrink, Attila Cangi, Sebastian Göde, Zuzana Konôpková, Mikako Makita, Mikhail Mishchenko, Motoaki Nakatsutsumi, Kushal Ramakrishna, Lisa Randolph, Sebastian Schwalbe, Jan Vorberger, Lennart Wollenweber, Ulf Zastrau, Tobias Dornheim, Thomas R. PrestonSubjects: Plasma Physics (physics.plasm-ph)
[ showing up to 2000 entries per page: fewer | more ]
Disable MathJax (What is MathJax?)
Links to: arXiv, form interface, find, physics, recent, 2405, contact, help (Access key information)